| Abstrakt: |
STAINSBY, W. N. and P. D. EITZMAN. Lactic acid output of cat gastrocnemius-plantaris during repetitive twitch contractions. Med. Sci. Sports Exerc.,Vol. 18, No. 6,668–673, 1986. Because fatigable, white (FF) muscle fibers have been reported to have a greater glycolytic capacity and a lower oxidative capacity than fatigue-resistant, red (FR and SR) muscle fibers, it is generally supposed that FF muscle fibers produce and therefore release more lactic acid into the blood during contractions than FR and SR muscle fibers. To test this supposition, the net lactic acid output, L, and O2uptake, VO2, were measured for the cat gastrocnemius-plantaris muscle during repetitive isometric contractions. The results obtained from this low metabolic capacity (FF, FR and SR muscles) were compared to results obtained previously in the high metabolic capacity (FR and SR muscles) of the same muscle group in the dog during similar contractions. Preliminary studies established that 1 twitch-2 s-1provided a similar VO2pattern during the contractions of cat muscle as 4 twitches-5-1produced in the dog muscle. The decline in VO2over a 30-min period of contractions was 12 to 18, as developed tension declined with fatigue. Thus, the contractions of the cat muscles were matched with the dog muscles in terms of the relative aerobic capacity and development of fatigue. During the 1 twitch-2 s-1twitches, the VO2reached 24.4 ± 1.41 (SE) μl.g-1min-tat 10 min of contractions. The VO2declined to 21.3 ± 2.3 μl.g-1.min-1by 30 min. The VO2and tension developed changed parallel to each other. The net L reached 0.21 ± 0.06 μmol.g-1.min-1at 10 min and fell to 0.13 ± 0.05 μmol.g-1.min by 30 min. Dog muscles reached VO2of 150 to 170 μg-1.min-1and had a peak net L of 0.7 to 1.2 μmol.g-1.min at 4 twitches-s-1.During repetitive contractions which were matched in terms of fatigue-producing propensity, the vO2and peak L of cat muscle are both lower than in dog muscle. A limited pilot study of higher frequency twitches and epinephrine infusion suggested that higher twitch rates and epinephrine increase L. |
